eal/arm: add vector memcpy for ARMv7

eal/arm: add vector memcpy for ARMv7

The SSE based memory copy in DPDK only support x86. This patch
adds ARM NEON based memory copy functions for ARM architecture.

The implementation improves memory copy of short or well aligned
data buffers. The following measurements show improvements over
the libc memcpy on Cortex CPUs.

               by X % faster
Length (B)   a15    a7     a9
   1         4.9  15.2    3.2
   7        56.9  48.2   40.3
   8        37.3  39.8   29.6
   9        69.3  38.7   33.9
  15        60.8  35.3   23.7
  16        50.6  35.9   35.0
  17        57.7  35.7   31.1
  31        16.0  23.3    9.0
  32        65.9  13.5   21.4
  33         3.9  10.3   -3.7
  63         2.0  12.9   -2.0
  64        66.5   0.0   16.5
  65         2.7   7.6  -35.6
 127         0.1   4.5  -18.9
 128        66.2   1.5  -51.4
 129        -0.8   3.2  -35.8
 255        -3.1  -0.9  -69.1
 256        67.9   1.2    7.2
 257        -3.6  -1.9  -36.9
 320        67.7   1.4    0.0
 384        66.8   1.4  -14.2
 511       -44.9  -2.3  -41.9
 512        67.3   1.4   -6.8
 513       -41.7  -3.0  -36.2
1023       -82.4  -2.8  -41.2
1024        68.3   1.4  -11.6
1025       -80.1  -3.3  -38.1
1518       -47.3  -5.0  -38.3
1522       -48.3  -6.0  -37.9
1600        65.4   1.3  -27.3
2048        59.5   1.5  -10.9
3072        52.3   1.5  -12.2
4096        45.3   1.4  -12.5
5120        40.6   1.5  -14.5
6144        35.4   1.4  -13.4
7168        32.9   1.4  -13.9
8192        28.2   1.4  -15.1

Signed-off-by: Vlastimil Kosar <kosar@rehivetech.com>
Signed-off-by: Jan Viktorin <viktorin@rehivetech.com>
Acked-by: David Marchand <david.marchand@6wind.com>